A topic in the Open Knowledge Graph — a free, open map of 15,290 topics and the order to learn them in.
Internal rural-urban migration and international migration from poor to rich countries are central to development. Migration allows workers to access higher-wage opportunities and reallocates labor from low to high-productivity sectors. Migration also creates social disruption, urban congestion, and brain drain when highly educated workers leave. Optimal migration policy balances these effects.
From the Lewis model of structural transformation, you know that development involves moving workers from low-productivity agriculture to higher-productivity industry and services. Labor migration is the mechanism through which this reallocation actually happens — people physically move from rural villages to cities, or from poor countries to rich ones, in search of better wages. At its core, migration is an investment decision: the migrant bears upfront costs (travel, job search, social dislocation) in exchange for expected future earnings gains, just as a student invests time in education for higher future wages.
Internal migration — typically rural-to-urban — is the most common form in developing countries and the engine of urbanization. When a young person leaves a farming village for a factory job in a growing city, two things happen simultaneously. First, the migrant earns more, because urban industrial wages exceed rural agricultural wages (this is the Lewis model's core prediction). Second, the economy becomes more productive in aggregate, because the same worker now produces more value. This is why urbanization and economic growth are so tightly correlated across countries: migration reallocates labor toward its most productive use.
International migration operates on the same logic at a larger scale. Wage gaps between rich and poor countries are enormous — a construction worker might earn ten times more in the Gulf states than in Bangladesh. Remittances, the money migrants send home, have become one of the largest financial flows to developing countries, exceeding foreign aid in many cases. For sending households, remittances provide insurance against crop failure and income to invest in children's education. For sending countries, remittances provide foreign exchange and can reduce poverty more directly than many aid programs.
But migration also generates costs that explain why it remains politically contentious. Urban areas in developing countries often grow faster than infrastructure and housing can accommodate, producing slums, congestion, and strained public services — the phenomenon captured by the Harris-Todaro model, where migration continues even when urban unemployment is high because migrants respond to expected rather than actual wages. Brain drain occurs when the most educated and skilled workers leave poor countries for rich ones, depriving the sending country of the human capital it invested in. A doctor trained at public expense in Ghana who practices in London represents a transfer of human capital from poor to rich. Whether the net effect of migration is positive depends on the balance between these gains and costs — and that balance varies enormously depending on who migrates, where they go, and whether they maintain economic ties to their origin.